"how to get an array of specific “key” in multidimensional array without looping" Code Answer

Since PHP 5.5, you can use array_column:

$ids = array_column($users, 'id');

This is the preferred option on any modern project. However, if you must support PHP<5.5, the following alternatives exist:

Since PHP 5.3, you can use array_map with an anonymous function, like this:

$ids = array_map(function ($ar) {return $ar['id'];}, $users);

Before ^{_{(Technically PHP 4.0.6+)}}, you must create an anonymous function with create_function instead:

$ids = array_map(create_function('$ar', 'return $ar["id"];'), $users);